Conventionally, an obstacle detection system for vehicle that is disposed in a vehicle for detecting the presence of an obstacle has been available. Normally the obstacle detection system for vehicle includes one ultrasonic sensor that includes one microphone to transmit/receive an ultrasonic wave (a so-called “single sonar”). This ultrasonic sensor detects a presence of an obstacle by transmitting an ultrasonic wave from the microphone and receiving the ultrasonic wave reflected by the obstacle. Moreover, the ultrasonic sensor measures the distance to the obstacle based on the time difference from the transmission to the reception of the ultrasonic wave.
In this obstacle detection system for vehicle however, the distance information from a vehicle to an obstacle can be acquired using the ultrasonic sensor, but the direction of the obstacle with respect to the vehicle cannot be acquired, therefore the positional information of the obstacle with respect to the vehicle cannot be acquired.
To solve this problem, there is an ultrasonic sensor where a microphone to transmit/receive an ultrasonic wave and a microphone dedicated to receiving an ultrasonic wave are integrated, and the distance and angle of the obstacle are calculated using trigonometric functions (a so called “dual sonar”) (e.g. see JP 2006-216066 A (hereafter called “Document 1”)).
However, a problem is that the detectable distance (distance for which an obstacle can be detected) is shorter when using an ultrasonic sensor having two microphones (dual sonar) compared with an ultrasonic sensor having one microphone (single sonar).